U.S. patent number 5,888,670 [Application Number 08/616,630] was granted by the patent office on 1999-03-30 for lithium secondary battery and electrodes therefor and method of forming the same.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Soichiro Kawakami.
United States Patent |
5,888,670 |
Kawakami |
March 30, 1999 |
Lithium secondary battery and electrodes therefor and method of
forming the same
Abstract
The present invention provides a lithium secondary battery which
has an anode, a separator, a cathode and an electrolyte and which
employs intercalation and deintercalation reaction of lithium ions.
The anode and/or the cathode of the secondary battery contains a
carbonaceous material having a structure in which pores are
oriented. The lithium secondary battery exhibits a high
charge-discharge efficiency, a high energy density and a long cycle
life. The present invention also provides a method of forming the
lithium secondary battery including the carbonaceous material
having oriented pores, by using an orienting material.
Inventors: |
Kawakami; Soichiro (Nara,
JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
|
Family
ID: |
26375773 |
Appl.
No.: |
08/616,630 |
Filed: |
March 15, 1996 |
Foreign Application Priority Data
|
|
|
|
|
Mar 17, 1995 [JP] |
|
|
7-058798 |
Feb 23, 1996 [JP] |
|
|
8-036691 |
|
Current U.S.
Class: |
429/231.4;
429/231.95 |
Current CPC
Class: |
H01M
10/0525 (20130101); H01M 4/587 (20130101); H01M
10/052 (20130101); Y02E 60/10 (20130101) |
Current International
Class: |
H01M
10/40 (20060101); H01M 10/36 (20060101); H01M
4/58 (20060101); H01M 010/40 () |
Field of
Search: |
;429/218
;423/447.1,447.2 ;502/180 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nuzzolillo; Maria
Assistant Examiner: Chaney; Carol
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. A lithium secondary battery at least comprising:
an anode;
a cathode;
a separator disposed between the anode and the cathode; and
an electrolyte,
wherein at least one of the anode and the cathode comprises a
powdered carbonaceous material having oriented pores.
2. A lithium secondary battery according to claim 1, wherein the
cathode comprises a carbonaceous material having oriented pores at
least as a component material, the carbonaceous material containing
a cathode active material being dispersed therein.
3. A lithium secondary battery according to claim 1, wherein the
anode comprises a collector and the carbonaceous material provided
on the collector.
4. A lithium secondary battery according to claim 1, wherein the
cathode comprises a collector and the carbonaceous material is
provided on the collector.
5. A lithium secondary battery according to claim 4, wherein the
carbonaceous material contains a cathode active material dispersed
therein.
6. A lithium secondary battery according to claim 3, wherein each
of the oriented pores has a lengthwise component in the direction
toward the collector.
7. A lithium secondary battery according to claim 4, wherein each
of the oriented pores has a lengthwise component in a direction
toward the collector.
8. A lithium secondary battery according to claim 3, wherein the
pores of the carbonaceous material are oriented perpendicularly or
substantially perpendicularly to a surface of the collector.
9. A lithium secondary battery according to claim 3, wherein the
pores of the carbonaceous material are oriented in parallel or
substantially parallel with the surface of the collector.
10. A lithium secondary battery according to claim 3, wherein a
surface of the collector on which a layer of carbonaceous material
is formed is treated by unidirectional rubbing.
11. A lithium secondary battery according to claim 4, wherein the
pores of the carbonaceous material are oriented perpendicularly or
substantially perpendicularly to a surface of the collector.
12. A lithium secondary battery according to claim 4, wherein the
pores of the carbonaceous material are oriented in parallel or
substantially parallel with a surface of the collector.
13. A lithium secondary battery according to claim 4, wherein a
surface of the collector on which a layer of carbonaceous material
is formed is treated by unidirectional rubbing.
14. A lithium secondary battery according to claim 3, wherein the
carbonaceous material is bonded to the collector by using a
binder.
15. A lithium secondary battery according to claim 4, wherein the
carbonaceous material is bonded to the collector by using a
binder.
16. A lithium secondary battery according to claim 1, further
comprising a housing for containing the anode, the cathode, the
separator and the electrolyte.
17. A lithium secondary battery according to claim 1, wherein the
pores have a diameter of 50 nm to 20 .mu.m.
18. A lithium secondary battery according to claim 1, wherein the
pores have a length of 50 .mu.m or less.
19. A lithium secondary battery according to claim 1, wherein the
carbonaceous material has a porosity of 10 to 90%.
20. A lithium secondary battery according to claim 17, wherein the
pores have a length of 50 .mu.m or less.
21. An electrode for a lithium secondary battery comprising:
a collector; and
an active material layer which is provided on the collector and
which contains a carbonaceous material having oriented pores, said
active material layer being able to be permeated by an
electrolyte.
22. An electrode for a lithium secondary battery according to claim
21, wherein the carbonaceous material is a powdered carbonaceous
material.
23. An electrode for a lithium secondary battery according to claim
21, wherein the carbonaceous material is bonded to the collector by
a binder.
24. An electrode for a lithium secondary battery according to claim
21, wherein the pores have a diameter of 50 nm to 20 .mu.m.
25. An electrode for a lithium secondary battery according to claim
21, wherein the pores have a length of 50 .mu.m or less.
26. An electrode for a lithium secondary battery according to claim
21, wherein the carbonaceous material has a porosity of 10 to
90%.
27. An electrode for a lithium secondary battery according to claim
24, wherein the pores have a length of 50 .mu.m or less.
28. An electrode for a lithium secondary battery according to claim
21, wherein the pores are oriented perpendicularly or substantially
perpendicularly to a surface of the collector.
29. An electrode for a lithium secondary battery according to claim
21, wherein the pores are oriented in parallel or substantially
parallel with a surface of the collector.
30. An electrode for a lithium secondary battery according to claim
21, wherein each of the pores has a lengthwise component in the
direction toward the collector.
31. An electrode for a lithium secondary battery according to claim
21, wherein the carbonaceous material further contains a cathode
active material.
32. A method of forming an electrode for a lithium secondary
battery comprising the step of:
preparing a carbonaceous material having pores, which are provided
on a collector, by burning a material containing an organic
polymeric material and an orienting material.
33. A method according to claim 32, further comprising the steps
of:
grinding the burned carbonaceous material to form a carbonaceous
material powder; and
bonding the carbonaceous material powder to the collector by using
a binder.
34. A method according to claim 32, wherein the material containing
the organic polymeric material and the orienting material is coated
on the collector and then burned.
35. A method according to claim 34, wherein the coating is
performed, after the collector is treated by applying an
amphiphilic molecule or an organic metal coupling agent to the
collector.
36. A method according to claim 34, wherein the coating is
performed, after the collector is treated by forming a polymer film
on the collector, and the polymer film is then rubbed
unidirectionally.
37. A method according to claim 34, wherein the coating is
performed, after forming an oriented film on the surface of the
collector by oblique deposition of a metal or organic polymeric
material by sputtering or vacuum deposition.
38. A method according to claim 32, wherein the orienting material
comprises a liquid crystal material.
39. A method according to claim 32, wherein the orienting material
contains at least one of diacetylene derivatives and polymers of
diacetylene derivatives.
40. A method according to claim 32, wherein the burning is carried
at a temperature within the range of 600.degree. to 3000.degree.
C.
41. A method according to claim 32, wherein the burning is carried
out in an atmosphere of inert gas.
42. A method according to claim 32, wherein the burning is carried
out in an atmosphere of nitrogen gas.
43. A method according to claim 41, wherein hydrogen gas is further
mixed in the inert gas.
44. A method according to claim 42, wherein hydrogen gas is further
mixed in the nitrogen gas.
45. A method according to claim 32, wherein an active material is
further mixed in the material containing the organic polymeric
material and the orienting material.
46. A method of producing a lithium secondary battery comprising
the steps of:
preparing a first electrode comprising a collector and a
carbonaceous material provided on the collector and having oriented
pores, the carbonaceous material being formed by burning a material
containing an organic polymeric material and an orienting
material;
disposing a second electrode opposite to the first electrode;
disposing a separator between the first and second electrodes;
and
sealing the first and second electrodes, the separator and an
electrolyte in a housing.
47. A method according to claim 46, further comprising the steps
of:
grinding the burned carbonaceous material to form a carbonaceous
material powder; and
bonding the carbonaceous material powder to the collector by using
a binder.
48. A method according to claim 46, wherein the material containing
the organic polymeric material and the orienting material is coated
on the collector and then burned.
49. A method according to claim 48, wherein the coating is
performed, after the collector is treated by applying an
amphiphilic molecule or an organic metal coupling agent to the
collector.
50. A method according to claim 48, wherein the coating is
performed, after the collector is treated by forming a polymer film
on the collector, and the polymer film is then rubbed
unidirectionally.
51. A method according to claim 48, wherein the coating is
performed, after forming an oriented film on the surface of the
collector by oblique deposition of a metal or organic polymeric
material by sputtering or vacuum deposition.
52. A method according to claim 46, wherein the orienting material
comprises a liquid crystal material.
53. A method according to claim 46, wherein the orienting material
contains at least one of diacetylene derivatives and polymers of
diacetylene derivatives.
54. A method according to claim 46, wherein the burning is carried
at a temperature within the range of 600.degree. to 3000.degree.
C.
55. A method according to claim 46, wherein the burning is carried
out in an atmosphere of inert gas.
56. A method according to claim 46, wherein the burning is carried
out in an atmosphere of nitrogen gas.
57. A method according to claim 55, wherein hydrogen gas is further
mixed in the inert gas.
58. A method according to claim 56, wherein hydrogen gas is further
mixed in the nitrogen gas.
59. A method according to claim 46, wherein an active material is
further mixed in the material containing the organic polymeric
material and the orienting material.
60. A lithium secondary battery comprising:
an anode;
a cathode;
a separator disposed between the anode and the cathode; and
an electrolyte able to permeate the surface of a carbonaceous
material,
wherein at least one of the anode and the cathode comprises the
carbonaceous material on a collector, the carbonaceous material
having pores oriented perpendicularly or substantially
perpendicularly to the collector.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lithium secondary battery and
electrodes therefor and a method of forming the same. More
particularly, the present invention relates to a lithium secondary
battery which prevents dendritic deposition of lithium metal from
occurring due to repeated charge and discharge and electrodes
therefor and a method of forming the same.
2. Description of the Related Art
In recent years, the amount of CO.sub.2 gas contained in atmosphere
has been increasing, and it has been thus predicted that global
warming occurs due to the greenhouse effect of CO.sub.2 gas. It is
therefore difficult to newly construct a thermal power plant which
converts energy generated by burning fossil fuel such as petroleum
or coal into electrical energy and which discharges a great amount
of CO.sub.2 gas.
In order to perform thermal power generation with a highest
efficiency, it is preferable to operate the plant under constant
conditions. Since the generated energy cannot be rapidly changed,
the generated energy is controlled to providing power consumption
in the daytime during which factories are generally consume a great
amount of power. Under the present conditions, therefore, the
generated power is wasted in the night during which power
consumption decreases. It is thus proposed that, in order to
effectively employ the electrical power generated by generators in
a thermal power plant, the power generated at nighttime stored in
secondary batteries installed in general homes, and is used in the
daytime when the power consumption is increased, for leveling
loads. This is known as load leveling. It is thus eagerly desired
to develop secondary batteries which can be used for the load
leveling.
It is also expected to develop high-energy density secondary
batteries with excellent utility for electric vehicles which
discharge no air pollutants such as carbon oxides (COx), nitrogen
oxides (NOx), hydrocarbon (CH) and particles during driving.
Further, it is of urgent necessity to develop smaller secondary
batteries which are more lighter weight and have higher
performance, and which are used as power supplies for portable
apparatus such as book-type personal computers, word processors,
video cameras and portable telephones.
Since the reversible electrochemical lithium-graphite intercalation
reaction was reported in JOURNAL OF THE ELECTROCHEMICAL SOCIETY
117,222 (1970), development of rocking chair type secondary
batteries, i.e., "lithium ion batteries", as an example of small,
lightweight and high-performance secondary batteries has proceeded
in which carbon and an intercalation compound containing lithium
ions are used as an anode active material and a cathode active
material, respectively, so that lithium is intercalated into the
carbon layer and stored therein by charge reaction. Some of such
lithium ion batteries are being brought into practical use. In
these lithium ion batteries, carbon serving as a host material for
intercalating lithium as a guest material into the layer is used as
the anode material so as to inhibit the growth of lithium dendrite
during charge, thereby achieving long life in a charge-discharge
cycle.
Since a secondary battery having long life can be achieved, as
described above, the application of various types of carbon to
anodes has been extensively proposed and investigated. A secondary
battery is proposed in U.S. Pat. No. 4,702,977 in which a
carbonaceous material having a hydrogen/carbon atomic ratio of less
than 0.15, a (002) facing of 0.337 nanometer or more, and a
crystallite c-axis size of 15 nanometer or less is used for an
anode, and alkali metal ions such as lithium ions are used. Another
secondary battery is proposed in U.S. Pat. No. 4,959,281 (Japanese
Patent Laid-Open No. 2-66856) in which a carbonaceous material
having a (002) facing of 0.370 nanometer or more, a true density of
less than 1.70 g/cm.sup.3 and no exothermic peak at 700.degree. C.
or more in differential thermal analysis in an air stream is used
for an anode.
Examples of various types of carbon which are being investigated
for use as battery anodes include carbon fibers (Denkikagaku, Vol.
57, p614 (1989)), mesophase microbeads (Extended Abstracts of The
34th Battery Symposium in Japan, p77 (1993)), natural graphite
(Extended Abstracts of The 33th Battery Symposium in Japan, p217
(1992)), graphite whiskers (Extended Abstracts of The 34th Battery
Symposium in Japan, p7 (1993)), and the burning product of furfuryl
alcohol resin (Extended Abstracts of The 58th Annual Meeting of the
Electrochemical Society of Japan, p158 (1991)).
However, a lithium ion battery which uses carbonaceous material as
an anode active material for storing lithium and which has a
discharge capacity exceeding the theoretical capacity of a graphite
intercalation compound for storing one lithium atom for six carbon
atoms, which permits stable discharge after repetition of charge
and discharge, has not been yet obtained. The lithium ion battery
using carbonaceous material as an anode active material thus has a
long cycle life and a battery energy density lower than that of a
lithium battery which uses a lithium metal as an anode active
material.
It is difficult to bring a high-capacity lithium storage battery
which uses a lithium metal for an anode into practical use because
of the difficulties in preventing the occurrence of lithium
dendrite, which mainly causes internal shorts, due to repetition of
charge and discharge. When an anode and a cathode are
short-circuited by the growth of lithium dendrite, heat is
generated by consumption of the energy of the battery in the
short-circuited portion within a short time, and gas is thus
generated by decomposition of a solvent of an electrolyte. This
causes an increase in the inner pressure of the battery and thus
accidental damage to the battery.
A method has been proposed as a measure against this in which a
lithium alloy such as lithium-aluminum is used for an anode for
suppressing the reactivity of lithium. However, this method
exhibits an unsatisfactory cycle life, and has not been brought
into extensive practical use.
On the other hand, a high-energy density lithium secondary battery
which has an energy density lower than that of a lithium primary
battery and which uses an aluminum foil having an etched surface as
an anode is reported in JOURNAL OF APPLIED ELECTROCHEMISTRY 22,
620-627 (1992). However, when a cycle of charge and discharge is
repeated up to a practical range, cracks occur in the aluminum foil
due to repeated expansion and contraction, thereby deteriorating
the current collecting properties and causing the growth of
dendrite. Thus, a secondary battery having a cycle life which
permits use at a practical level cannot be obtained.
Therefore, it is eagerly desired to develop an anode material which
has a long life and an energy density higher than that of a
carbonaceous anode material which is currently put into practical
use.
It is also necessary for realizing a high-energy density secondary
battery to develop a cathode material. Under the present
conditions, a lithium-transition metal oxide is mainly used as a
cathode active material. However, the discharge capacity attained
is only 40 to 60% of the theoretical capacity.
For lithium secondary batteries including "lithium ion batteries"
which use lithium ions as a guest in charge-discharge reaction, it
is strongly desired to develop an anode and a cathode which have a
cycle life within a practical range, and capacity higher than that
of an anode comprising carbonaceous material and a cathode
comprising transition metal oxide, which are presently brought into
practical use.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a lithium
secondary battery which uses lithium as an anode active material
and which has a high energy density and a long cycle life, and
electrodes for the lithium secondary battery, and a method of
forming the same.
Another object of the present invention is to provide a lithium
secondary battery which is capable of smoothly producing
electrochemical reaction with a lower current density accompanied
with charge and discharge, and which is capable of passing a large
current during charge and discharge, and electrodes for the lithium
secondary battery and a method of forming the same.
A further object of the present invention is to provide a lithium
secondary battery having a high charge-discharge efficiency, and
electrodes for the lithium secondary battery and a method of
forming the same.
In accordance with one aspect of the invention a lithium secondary
battery comprising at least an anode, a cathode, a separator
disposed between the anode and the cathode and an electrolyte,
wherein at least one of the anode and the cathode comprises a
carbonaceous material having oriented pores.
According to another aspect of the present invention, there is
provided an electrode for a lithium secondary battery which
comprises a current collector, and an active material layer
disposed on the current collector and comprising a carbonaceous
material having oriented pores.
In a further aspect of the present invention, there is provided a
method of forming an electrode for a lithium secondary battery
comprising a current collector, and a carbonaceous material
disposed on the current collector and having oriented pores. The
method includes the step of burning a mixed material containing an
organic polymer material and an orienting material to form the
carbonaceous material.
According to a still further aspect of the present invention, there
is provided a method of forming a lithium secondary battery
comprising the steps of preparing a first electrode comprising a
current collector and a carbonaceous material with oriented pores
which is disposed on the current collector and which is formed by
burning a mixed material containing an organic polymer material and
an orienting material, disposing a second electrode opposite to the
first electrode, disposing a separator between the first and second
electrodes, and then sealing both electrodes, the separator and an
electrolyte in a housing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic sectional view illustrating the structure of
an anode which can preferably be used for a secondary battery of
the present invention;
FIG. 2 is a schematic sectional view illustrating the structure of
a cathode which can preferably be used for a secondary battery of
the present invention;
FIG. 3 is a schematic sectional view illustrating a carbonaceous
material powder which can preferably be used for an anode of a
secondary battery of the present invention;
FIG. 4 is a schematic sectional view illustrating a carbonaceous
material powder which can preferably be used for a cathode of a
secondary battery of the present invention;
FIG. 5 is a schematic sectional view illustrating the structure of
an electrode which can preferably be used for a secondary battery
of the present invention;
FIG. 6 is a schematic drawing illustrating an example of the basic
construction of a secondary battery which uses the electrode shown
in FIGS. 1, 2 or 5;
FIG. 7 is a schematic partially sectional view illustrating an
example of a single-layer flat battery; and
FIG. 8 is a schematic partially sectional view illustrating an
example of a spiral type cylindrical battery.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to the structure of an electrode (an
anode or a cathode) of a lithium secondary battery comprising at
least an anode, a cathode, a separator disposed between the anode
and the cathode, and an electrolyte. The lithium secondary battery
also comprises a carbonaceous material having oriented pores at
least as a constituent material. The carbonaceous material having
oriented pores can be formed by the step of mixing an organic
polymer material and an orientating material.
In the present invention, the cathode carbonaceous material
functions to assist conduction for collecting current from a
cathode active material used as a host material for lithium ions,
and the anode carbonaceous material functions as the host material
for the lithium ions. Since the cathode and/or the anode comprises
the carbonaceous material at least having a structure in which
pores are oriented, the electrolyte easily permeates the electrode.
As a result, it is possible to decrease the impedance of the
battery, improve the charge-discharge efficiency and prevent
secondary reaction during charge and discharge, thereby suppressing
deterioration in the electrodes. It is thus possible to realize a
lithium secondary battery having a high capacity and a long cycle
life.
Further, when the cathode comprises the carbonaceous material in
which the cathode active material as the host material for lithium
ions is intercalated, since the carbonaceous material functioning
as a conduction auxiliary material is present nearer the cathode
active material than a cathode formed by coating a mixture
containing a cathode active material, a conduction auxiliary and a
binder, the higher collecting ability can be attained. As a result,
the utilization of the cathode can be increased, and a
high-capacity lithium secondary battery can thus be realized.
If the pores of the carbonaceous material layer are oriented at
least in the direction toward the surface of the collecting
electrode, preferably perpendicular or substantially perpendicular
thereto, the electrolyte can easily permeates the electrode. It is
consequently possible to perform rapid charge and discharge. In the
anode, lithium can be deposited on the pore surfaces and in the
pores other than between the carbonaceous material layers by charge
reaction, thereby preventing the growth of dendritic lithium metal
deposition. It is thus possible to realize a lithium secondary
battery having a higher capacity. On the other hand, if the pores
of the carbonaceous material layer are oriented at least in
parallel with the surface of the collecting electrode, it is
possible to increase the flexural strength of the electrode, and
suppress the separation of the active material layer from the
collecting electrode even when the electrode is wound in a spiral
form.
If a collector having a rubbed surface is used as a collector (a
collector of the cathode and/or the anode) on which a carbonaceous
material layer is formed, it is possible to more effectively
suppress the separation of the active material layer.
The method of forming the electrodes for the lithium secondary
battery of the present invention comprises mixing an orientating
material and an organic polymer material which can be carbonized or
graphitized by burning, and burning the organic polymer material to
form the carbonaceous material. Pores oriented in the carbonaceous
material can easily be formed by any desired method for removing
the orientating material after burning. The organic polymer
material readily coordinates with a carbon-carbon double bond, an
ether bond, an ester bond, or a polar group such as a benzene ring,
which is generally possessed by the orientating material, to obtain
the carbonaceous material having a high degree of graphitization.
As a result, when the carbonaceous material is used as the host
material of the anode for intercalating and deintercalating lithium
ions, the high-capacity anode can be formed. Therefore, with the
lithium secondary battery comprising the electrode comprising the
carbonaceous material formed by this method and used for an anode
active material layer, a high electric capacity and energy density
can be attained.
In addition, the step of coating a coating solution, which is
obtained by mixing the orientating material in a solution of the
organic polymer material, on a substrate which was subjected to
treatment of preorientation facilitates orientation of the
orientating material during the formation of the carbonaceous
material, thereby simply obtaining the carbonaceous material having
oriented pores.
The present invention is described in detail below with reference
to the drawings.
FIG. 1 is a schematic longitudinal sectional view illustrating an
anode which is preferably used for the secondary battery of the
present invention. FIG. 2 is a schematic longitudinal sectional
view illustrating a cathode which is preferably used for the
secondary battery of the present invention.
In FIGS. 1 and 2, reference numeral 100 denotes a collector;
reference numeral 101, a carbonaceous material; reference numeral
102, oriented pores; reference numeral 103, a cathode active
material; reference numeral 104, an active material layer;
reference numeral 105, an anode; and reference numeral 106, a
cathode.
Referring FIGS. 1 and 2, the carbonaceous material 101 having the
oriented pores 102 is provided on the collector 100. The pores 102
are oriented so that the lengthwise components thereof are in the
direction toward the collector 100, and preferably oriented in the
direction perpendicular or substantially perpendicular to the
collector 100.
The anode 105 shown in FIG. 1 has a structure in which the active
material layer 104 comprising the carbonaceous material 101 having
the oriented pores 102 is provided at least on a portion of the
surface of the collector 100, which contacts an electrolyte
opposite to a cathode (not shown). The cathode 106 shown in FIG. 2
has a structure in which the active material layer 104 comprising
the carbonaceous material 101 having the oriented pores 102 and
containing the cathode active material 103 dispersed therein is
provided at least on a portion of the surface of the collector 100,
which contacts an electrolyte opposite to an anode (not shown).
Description will now be made of a preferred embodiment which uses a
powdered carbonaceous material having oriented pores apart from the
case in which a carbonaceous material layer having oriented pores
is formed at least on side of the collector, as shown in FIGS. 1
and 2.
FIG. 3 is a conceptual sectional view of a powdered carbonaceous
material having oriented pores, and FIG. 4 is a conceptual
sectional view of the case in which an active material is dispersed
in a powdered carbonaceous material having oriented pores.
In FIGS. 3 and 4, reference numeral 201 denotes a carbonaceous
material; reference numeral 202, oriented pores; reference numeral
203, a carbonaceous material powder for an anode; reference numeral
204, a cathode active material; and reference numeral 205, a
carbonaceous material powder for a cathode.
As shown in FIG. 4, the dispersed active material 204 is provided
for the cathode.
FIG. 5 is a conceptual sectional view illustrating an example of
the structure of an electrode (an anode or cathode) comprising the
carbonaceous material powder 203 or 205 shown in FIGS. 3 or 4.
As shown in FIG. 5, an electrode (an anode or cathode) 207
comprises an active material layer 206 which is formed on a
collector 200 by bonding the carbonaceous material powder 203 or
205 for the anode or cathode to the collector 200 using a binder
208.
The active material layer 206 may be formed on not only one side of
the collector 200 but also both sides thereof or a main surface of
the collector 200. This applies to the active material layer 104
shown in FIGS. 1 and 2.
The conceptual structure of the secondary battery of the present
invention is described with reference to FIG. 6.
In FIG. 6, reference numeral 301 denotes an anode (electrode);
reference numeral 302, a cathode (electrode); reference numeral
303, an electrolyte; reference numeral 304, a separator; reference
numeral 305, an anode terminal; reference numeral 306, a cathode
terminal; and reference numeral 307, a housing.
As shown in FIG. 6, the anode 301 and the cathode 302 are disposed
in the electrolyte 303 held in the housing 307 opposite to each
other through the separator 304. The separator 304 is provided for
preventing internal shorts due to the contact between the anode 301
and the cathode 302.
The anode 301 and the cathode 302 respectively have the structures
shown in FIGS. 1 and 2 or 5. The anode terminal 305 and the cathode
terminal 306 are electrically connected to the collectors of the
anode 301 and the cathode 302, respectively. The collectors of the
electrodes may be respectively used as the anode terminal 305 and
the cathode terminal 306. The anode terminal 305 and the cathode
terminal 306 or at least a portion of the collectors may form at
least a portion of the housing 307.
Each of the components of the battery is described in detail
below.
[Electrode]
In the present invention, each of the electrodes comprises the
carbonaceous material having oriented pores and formed at least on
the collector.
A method of forming the anode shown in FIG. 1 in accordance with a
preferred embodiment is described below.
An orienting material is mixed in a solution of an organic polymer
material which is carbonized or graphitized by burning to prepare
paste.
The paste prepared by the above step is then coated on the
collector, and the organic polymer material in the paste is
solidified under conditions for orienting the orienting
material.
The orienting material is then removed from the solidified organic
polymer material.
The remaining organic polymer material is carbonized or graphitized
by burning under an inert gas or nitrogen gas to form the
anode.
For example, a coater coating method or a screen printing method
can be used for coating the paste. As a method of solidifying the
organic polymer material, a method of removing a solvent and then
drying, or a method of producing crosslinking reaction can be used.
The orientation conditions depend upon the orienting material
used.
The cathode shown in FIG. 2 can be formed by the same procedure as
the above procedure for forming the anode except that the cathode
active material is mixed in the paste in the first step.
A method of producing the cathode comprising the carbonaceous
material powder for a cathode shown in FIG. 4 in accordance with a
preferred embodiment is described below.
An orienting material and a cathode active material are mixed in a
solution of an organic polymer material which is carbonized or
graphitized by burning to prepare paste.
The organic polymer material in the paste prepared by the above
step is solidified under conditions for orienting the orienting
material.
The orientating material is then removed from the solidified
organic polymer material.
The remaining organic polymer material is carbonized or graphitized
by burning under an inert gas or nitrogen gas to prepare the
carbonaceous material having oriented pores.
The carbonaceous material is then ground under an inert gas or
nitrogen gas to prepare a carbonaceous material powder containing
the cathode active material dispersed therein.
The carbonaceous material powder, a binder and a solvent are mixed
to prepare paste.
The paste is coated on the collector, and then dried to prepare the
cathode.
The anode active material shown in FIG. 3 and the anode shown in
FIG. 5 can be formed by the same procedure as the above procedure
for forming the cathode comprising the carbonaceous material powder
shown in FIG. 4 except that the step of mixing the cathode active
material in the paste is eliminated.
When a lithium battery is assembled by using the anode and cathode,
the anode and cathode must be sufficiently dehydrated and dried.
Dehydration is preferably performed by heating under reduced
pressure.
(Organic Polymer Material as a Raw Material for the Carbonaceous
Material)
A material which is carbonized or graphitized by burning is used as
the organic polymer material as a raw material for the carbonaceous
material having the oriented pores, which is a component of the
anode or cathode of the present invention. Preferable examples of
such a material include poly(vinylalcohol), poly(furfurylalcohol),
poly(vinylacetate), polyacrylonitrile, poly(para-phenylene),
poly(para-phenylenesulfide), poly(para-phenylenevinylene),
polythienylene, polydithienylpolyene, poly(vinylnaphthalene),
poly(acenaphthylene), poly(vinylchloride) and the like.
The burning temperature of the organic polymer material is
preferably 600.degree. to 3000.degree. C. It is preferable that the
organic polymer material is burned under an inert gas such as an
argon gas or helium gas or a nitrogen gas, and that when the
collector might be oxidized, hydrogen gas is appropriately mixed
for suppressing oxidation.
(Orienting-Material)
Preferable examples of the orientating material used as a raw
material for preparing the carbonaceous material having the
oriented pores and used as a component of the anode or cathode of
the present invention include (1) liquid crystal materials, and (2)
diacetylene derivatives and diacetylene derivative polymers.
(1) Liquid Crystal Materials
The liquid crystal materials include thermotropic materials each of
which forms a liquid crystal layer through a melting process, and
lyotropic materials which exhibit crystallizability in the presence
of a solvent. Liquid crystals exhibiting various types of
orientations, such as nematic liquid crystals, cholesteric liquid
crystals, smectic liquid crystals, discotic liquid crystals and
ferroelectric liquid crystals which show spontaneous polarization
can be used.
Preferred examples of the liquid crystal materials which can be
used in the present invention are given below. Examples of nematic
liquid crystals include p-methoxybenzylidene-p'-n-butylaniline,
p-ethoxybenzylidene-p'-n-butylaniline, octyloxy-cyanobiphenyl,
p-n-phenyl-p'-cyanobiphenyl and the like. Examples of cholesteric
liquid crystals include cholesteryl nonanate,
hexaalkanoyloxybenzene, tetraalkanoyloxy-p-benzoxine,
hexaalkoxytriphenylene, hexaalkanoyloxytriphenylene,
hexaalkanoyloxytoluxene, hexaalkanoylrufigallol,
2,2',6,6'-tetraaryl-4,4'-bipyranylidene,
2,2',6,6'-tetraaryl-4,4'-bithiopyranylidene, substituted benzoate
of hexahydrotriphenylene and the like. Examples of smectic liquid
crystals include butyloxybenzylidene-octylaniline,
p-cyanobenzylidene-p'-n-octyloxyaniline and the like. Examples of
discotic liquid crystals include triphenylene-hexa-n-dodecanoate,
2,3,6,7,10,11-hexamethoxytriphenylene and the like. Examples of
ferroelectric liquid crystals include azomethine compounds
(Schiff's compounds), azoxy compounds, esters, .gamma.-lactone
compounds, mixtures of chiral compounds, mixtures of achiral liquid
crystals and chiral compounds, and the like. Examples of polymeric
liquid crystals include polystyrene-polyethylene oxide block
copolymers, poly-.gamma.-benzyl-L-glutamate, hydroxypropyl
cellulose, poly(p-phenylene terephthalamide), poly[(ethylene
terephthalate)-co-1,4-benzoate], poly(4,4'-dimethylazoxybenzene
dodecanediol), poly(oligoethylene azoxybenzoate), poly(p-benzamide)
and the like.
(2) Diacetylene Derivatives and Diacetylene Derivative Polymers
Examples of diacetylene derivatives include 2,4-hexadiyne-1,6-diol,
diacetyelenecarbonic acid,
2,4-hexadiyne-1,6-diol-bis-phenylurethane, ortho- or
meta-substituted diphenyldiacetylene,
3,6,13,16-tetraoxaoctadeca-8,10-diine-1,18-diol and the like.
Diacetylene derivative polymers having a plane structure can be
obtained by solid phase polymerization of diacetylene derivatives
by a method of heating, ultraviolet irradiation, electron beam
irradiation or radiation. Namely, the oriented diacetylene
derivative polymers can be obtained by solid phase polymerization
of diacethylene derivatives.
(Method of Orienting the Orienting Material)
Orientation of the orienting material is controlled by applying an
electric field, a magnetic field or stress, performing orientation
of the surface of the collector as a substrate, heating or cooling,
and appropriately selecting an optimum solvent and an optimum
concentration.
(Orientation of the Substrate Surface)
Methods of orienting the substrate surface are roughly classified
into vertical (homeotropic) orientation, parallel (homogeneous)
orientation and oblique orientation. Examples of vertical
orientation methods include a physical adsorption method using an
amphiphilic molecule of p-(octyloxy)-p'-hydroxyazobenzene,
dimethylhexadecylammonium bromide, didodecyl
N-[11-bromoundecanoyl]-L-glutamate, hexadecyltributylphosphonium
bromide, stearyltributylphosphonium bromide, lecithin,
cetyltrimethylammonium bromide or the like; and a chemical
adsorption method using an organic metal coupling agent such as
stearyltrichlorosilane or the like. Examples of parallel
orientation methods include a method of rubbing, in one direction,
a polymeric film such as polyimide or polyvinyl alcohol, which is
laminated on the surface of the collector, with a cloth or paper; a
method of grinding, in one direction, the surface of the collector
with a material harder than the substrate. Examples of oblique
orientation methods include a method of forming an oriented film on
the surface of the collector by oblique deposition of a metal or an
organic polymeric material by sputtering or vacuum deposition such
as electron beam deposition.
Removal of the Orienting Material
A solvent extraction method or thermal decomposition method can be
used as the method of removing the orienting material in the method
of producing the carbonaceous material having oriented pores.
(Pores of the Carbonaceous Material)
The diameter of the oriented pores of the carbonaceous material
used for forming the electrodes of the present invention
significantly depends upon the types and mixing ratio of the
organic polymer material and the orienting material used in
formation, and the type and ratio of the solvent added. The optimum
ranges of the diameter and volume of the pores of the carbonaceous
material are determined by the ease of preparation of the
carbonaceous material, and the mechanical strength and
charge-discharge characteristics of the electrodes prepared, and
not readily determined. The oriented pores of the carbonaceous
material which forms an electrode of the present invention may
include micropores having a diameter of 2 nanometers or less, which
is measured by a gas adsorption method, and mesopores having a
diameter of 2 to 5 nanometers. However, macropores having a
diameter of 50 nanometers or more are considered to significantly
affect an improvement in the charge-discharge characteristics of
rapid charge. In the present invention, therefore, the diameters of
the oriented pores are mainly preferably within the range of 50
nanometers to 20 microns, more preferably within the range of 50
nanometers to 10 microns. The average diameter of the pores is
further preferably 5 microns or less. When the electrodes are wound
in a spiral form, the length of the oriented pores is preferably 50
microns or less in order to prevent cracks in the electrodes
depending upon the radius of curvature, and to improve the life
performance and charge-discharge efficiency of the battery by
improving the property of holding the electrolyte inside the
surface of the electrode.
When the volume of the pores of the carbonaceous material which
forms the electrodes of the present invention are excessively
small, the electrolyte hardly permeates the electrodes. When the
volume of the pores of the carbonaceous material is excessively
large, the strength of the electrodes is decreased, and the
resistance of the electrodes is increased, thereby increasing a
current loss. The optimum porosity depends upon the diameter and
the distribution state of the pores, and the thickness of the
anode. Therefore, the porosity of the anode except the collector is
preferably within the range of 10 to 90%, and more preferably
within the range of 20 to 80%. The porosity corresponding to the
volume of the pores can be measured by a mercury porosimeter or
observation on an electron microscope. The porosity can also be
determined by calculation from the volumes of the orienting
material and the solvent mixed.
(Collectors of the Anode and Cathode)
The collectors serving as the collecting electrodes of the anode
and cathode of the present invention function to efficiently supply
a current to be consumed by electrode reaction during charge and
discharge or to collect the current generated by the electrode
reaction. The material used for forming the collectors of the anode
and cathode preferably has high conductivity and is inert to the
electrode reaction. It is also preferable to use a material which
causes no problem in the step of forming the carbonaceous material
and the step of forming the active material layer. Preferable
examples of such materials include nickel, titanium, copper,
aluminum, stainless steel, platinum, palladium, gold, zinc, various
alloys, and composite metals comprising at least two of these
metals. Examples of shapes which can be used for the collectors
include a plate, a foil, a mesh, a sponge, fibers, a punching
metal, an expanded metal and the like.
(Cathode Active Material)
As the cathode active material used as the host material for
intercalating and deintercalating lithium ions in the present
invention, a transition metal oxide, a transition metal sulfide, a
lithium-transition metal oxide, or a lithium-transition metal
sulfide is preferably used. Examples of transition metals of
transition metal oxides and transition metal sulfides include Sc,
Y, lanthanides, actinides, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn,
Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au, which
are elements partially having d-shell or f-shell. More
particularly, the metals in the first transition series, e.g., Ti,
V, Cr, Mn, Fe, Co, Ni and Cu are preferably used.
(Binder)
When the binder is used for forming the cathode or anode of the
present invention, for example, a polyolefin such as polyethylene
or polypropylene, or fluororesin such as polyvinylidene fluoride or
tetrafluoroethylene polymer is preferably used as the binder.
(Separator)
The separator used in the present invention functions to prevent
internal shorts between the anode and the cathode, and sometimes
functions to hold the electrolyte.
The separator must have pores which permit movement of lithium
ions, and must be insoluble and stable in the electrolyte. Thus,
examples of materials which are preferably used for such a
separator include glass, polyolefins such as polypropylene and
polyethylene, fluororesins, and materials having a micropore and
nonwoven fabric structure. A metal oxide film having micropores and
a resin film compounded with a metal oxide can also be used. More
particularly, when a metal oxide film having a multi-layer
structure is used, dendritic deposited lithium metal hardly
permeates the separator, thereby obtaining the effect of preventing
internal shorts. The use of a fluororesin film which is a flame
retardant material, glass which is a non-combustible material, or a
metal oxide film can further increase safety.
(Electrolyte)
The methods of using the electrolyte in the present invention
include the following three methods;
(1) The method of using the electrolyte as it is.
(2) The method of using a solution of the electrolyte.
(3) The method of using the electrolyte which is fixed by adding a
gelling agent such as a polymer to a solution.
An electrolyte solution obtained by dissolving the electrolyte in a
solvent is generally held by the separator. It is necessary that
the conductivity of the electrolyte at 25.degree. C. be preferably
1.times.10.sup.-3 S/cm or more, and more preferably
5.times.10.sup.-3 S/cm or more.
In the lithium battery which uses lithium as the anode active
element, the electrolytes and solvents below are preferably used.
Examples of electrolytes include acids such as H.sub.2 SO.sub.4,
HCl and HNO.sub.3, salts comprising lithium ions (Li.sup.+) and
Lewis acid ions (BF.sub.4 --, PF.sub.6 --, ClO.sub.4 --, CF.sub.3
SO.sub.3 -- and BPh.sub.4 -- (Ph: phenyl group)), and salt mixtures
thereof. Salts comprising cations such as sodium ion, calcium ion
and tetraalkylammonium ion, and the Lewis acid ions can also be
used. These salts are preferably sufficiently dehydrated and
deoxidized by heating under reduced pressure.
Examples of solvents which are preferably used for the electrolyte
include acetonitrile, benzonitrile, propylenecarbonate,
ethylenecarbonate, dimethylcarbonate, diethylcarbonate,
dimethylformamide, tetrahydrofuran, nitrobenzene, dichloroethane,
diethoxyethane, 1,2-dimethoxyethane, chlorobenzene,
.gamma.-butyrolactone, dioxolan, sulfolan, nitromethane,
dimethylsulfide, dimethylsulfoxide, methylformate,
3-methyl-2-oxazolidinone, 2-methyltetrahydrofuran, 3-propylsydnone,
sulfurdioxide, phosphorylchloride, thionylchloride,
sulfurylchloride, and solvent mixtures thereof.
These solvents are preferably dehydrated by activated alumina,
molecular sieves, phosphoruspentaoxide or calciumchloride. Some of
the solvents are preferably subjected to removal of impurities and
dehydrated by distillation in coexistence with an alkali metal in
an inert gas.
It is preferable for preventing a leakage of the electrolyte to gel
the electrolyte. A polymer which absorbs the solvent of the
electrolyte and swells is preferably used as a gelling agent.
Examples of such polymers include poly(ethyleneoxide),
poly(vinylalcohol), polyacrylamide and the like.
Lithium used as the anode active element is intercalated into the
anode active material layer by charging the resultant battery.
(Shape and Structure of Battery)
Examples of shapes of the battery of the present invention include
a flat shape, a cylindrical shape, a prismatic shape, a sheet shape
and the like. Examples of structures of the battery include a
single-layer, multi-layer and spiral (jelly roll) structures and
the like. Of these shapes and structure, a spiral type cylindrical
battery is preferred because the anode and the cathode are wound
with the separator therebetween so that the electrode areas can be
increased, and a large current can be caused to flow during charge
and discharge. A prismatic battery is preferred in the point that a
space for storing an apparatus which contains the secondary battery
can effectively be utilized.
The shape and structure of the battery in accordance with
embodiments are described in detail below with reference to FIGS. 7
and 8. FIG. 7 is a schematic partial sectional view of a
single-layer flat battery, and FIG. 8 is a schematic partial
sectional view of a spiral type cylindrical battery.
In FIGS. 7 and 8, reference numeral 400 denotes an anode collector;
reference numeral 401, an anode active material layer; reference
numeral 402, an anode; reference numeral 403, a cathode active
material layer; reference numeral 405, an anode terminal (an anode
cap); reference numeral 406, a cathode can; reference numeral 407,
a separator and electrolyte; reference numeral 408, a cathode;
reference numeral 410, an insulating packing; and reference numeral
411, an insulating plate.
An example of the method of assembling the batteries having the
structures shown in FIGS. 7 and 8 is described.
The anode active material layer 401 and the cathode active material
layer 403 are contained in the cathode can 406 with the separator
407 therebetween. At this time, in the battery having the structure
shown in FIG. 8, the anode active material layer 401 and the
cathode active material layer 403 are opposed to each other with
the separator 407 therebetween and then wound.
After the electrolyte is injected into the can 406, the anode cap
405 is disposed on the cathode can 406 through the insulating
packing 410. At least a portion of the cathode can 406 and/or the
anode cap 405 is then caulked to complete the battery.
It is preferred that the materials for the lithium battery are
prepared, and the battery is then assembled in dry air or dry inert
gas from which moisture is sufficiently removed.
Insulating Packing
Examples of materials which can be used for the insulating packing
410 of the present invention include polyolefins, fluororesins,
polyamide resins, polysulfone resins, and various types of rubber.
Methods of glass sealing, an adhesive, welding and soldering other
than "caulking" using a gasket such as the insulating packing shown
in FIGS. 7 and 8 can also be used as the method of sealing the
battery.
Various organic resin materials and ceramics which are chemically
stable in environments (for example, the temperature) where the
electrolyte and the battery are used, are preferably used as
materials for the insulating plate 411 shown in FIG. 8.
(Outer Can)
The outer can shown in FIGS. 7 and 8 corresponds to the cathode can
406 and the anode cap 405 of the battery. Stainless steel is
preferably used as material for the outer can. In particular, a
titanium clad stainless sheet, a copper clad stainless sheet and a
nickel-plated steel sheet are preferred.
Since the cathode can 406 and the anode cap 405 are also used as a
battery case (housing), as shown in FIGS. 7 and 8, the foregoing
stainless steel is preferable from the viewpoint of sufficient
strength. However, when the cathode can and the anode cap do not
serve as the terminal i.e., when the battery housing need not have
so much strength, a metal such as zinc, an alloy, plastic such as
polypropylene, and a composite material comprising a metal or glass
fibers and plastic other than stainless steel can also be used for
the housing.
(Safety Valve)
A safety valve is generally provided as a safety means for the case
where the internal pressure of the battery is increased. Examples
of the safety valve include rubber, a spring, a metallic ball, a
rupture foil and the like. Alternatively, the battery may be
designed so that a portion of a component of the battery,
particularly, the battery housing has low strength so as to be
first broken when the internal pressure is abnormally increased,
thereby allowing escape of the internal pressure.
The present invention is described in further detail below with
reference to examples. However, the present invention is not
limited to these examples.
EXAMPLE 1
This example relates to the formation of a lithium secondary
battery having the structure shown in FIG. 7 in which a
carbonaceous powder having oriented pores is used. The procedure
for forming each of the components of the battery and the assembly
of the battery are described below with reference to FIG. 7.
(1) Procedure for Forming the Anode
After a nematic liquid crystal,
p-methoxybenzylidene-p'-butylaniline, was added to an
N,N-dimethylformamide solution of polyvinyl alcohol and mixed
therewith, the resultant mixture was dropped in ethanol to prepare
precipitates. The thus-obtained precipitates were dried under
reduced pressure, gradually heated to 800.degree. C. and burned at
this temperature in a stream of argon gas, and then ground to
prepare a carbonaceous powder. Observation of the resultant
carbonaceous powder under an electron microscope showed oriented
pores having a diameter of 5 microns or less. The porosity of the
carbonaceous powder was 15%.
After 5 wt % of polyvinylidene fluoride was mixed with the
thus-obtained carbonaceous powder, N-methylpyrrolidone was added to
the resultant mixture to prepare paste. The thus-obtained paste was
coated on a copper foil and dried, and then dried at 150.degree. C.
under reduced pressure to form the anode.
(2) Procedure for Forming a Cathode
After electrolytic manganese dioxide and lithium carbonate were
mixed at a molar ratio of 1:0.4, the resultant mixture was heated
at 800.degree. C. to prepare lithium-manganese oxide. After 3% by
weight of carbonaceous powder of acetylene black and 5% by weight
of polyvinylidene fluoride were mixed with the thus-prepared
lithium-manganese oxide, N-methylpyrrolidone was added to the
resultant mixture to prepare paste. The thus-obtained paste was
coated on an aluminum foil and dried, and then dried at 150.degree.
C. under reduced pressure to prepare a cathode.
(3) Procedure for Forming the Electrolyte
Equivalent ethylene carbonate (EC) and dimethyl carbonate (DMC),
from which moisture was sufficiently removed, were mixed to prepare
a solvent. 1M (mol/l) lithium tetrafluoroborate was dissolved in
the resultant solvent to prepare the electrolyte.
(4) Separator
A microporous polyethylene film was used as the separator.
(5) Assembly of the Battery
The separator holding the electrolyte was held between the anode
and the cathode, and then inserted into the cathode can made of
titanium clad stainless steel. The insulating packing made of
polypropylene and the anode cap made of titanium clad stainless
steel were placed in that order on the cathode can, and the cathode
cap and the anode cap were caulked to form the lithium secondary
battery.
COMPARATIVE EXAMPLE 1
In this example, a secondary battery was formed by the same method
as in Example 1 except that the anode was prepared by a different
method.
(1) Procedure for Forming the Anode
Polyvinyl alcohol was gradually heated to 800.degree. C. and burned
at this temperature in a stream of argon gas, and then ground to
prepare a carbonaceous powder. Observation of the resultant
carbonaceous powder under an electron microscope showed no oriented
pores.
5 wt % of polyvinylidene fluoride was mixed with the resultant
carbonaceous powder, and N-methyl pyrrolidone was then added to the
resultant mixture to prepare paste. The thus-obtained paste was
coated on a copper foil and dried, and then dried at 150.degree. C.
under reduced pressure to prepare an anode.
A secondary battery was formed in the same manner as in Example 1
except the above-described treatment was performed.
X-ray diffraction of the carbonaceous powders which were used for
the anodes of Example 1 and Comparative Example 1 indicated that
the ratio of the half width (radian) of the (002) peak of the
carbonaceous powder of Example 1 to the half width of the
carbonaceous powder of Comparative Example 1 is 0.45, and that the
carbonaceous powder of Example 1 is more graphitized than the
carbonaceous powder of Comparative Example 1.
The performance of the batteries of Example 1 and Comparative
Example 1 was evaluated with respect to energy density per unit
weight of a battery and cycle life, which were measured in a
charge-discharge cycle test. The cycle test was carried out under
conditions that one cycle comprises charge and discharge of 1 C
(current equal to capacity/hour) based on the electrical capacity
calculated from the cathode active material used, and a rest time
of 30 minutes. A charge-discharge test of a battery was carried out
by using HJ-106M produced by Hokuto Denko Co. The charge-discharge
test was started from charge, the battery capacity corresponding to
the discharge amount by three cycles, and the cycle life
corresponding to the number of cycles when the battery capacity was
less than 60%. In the lithium batteries, the charge cut-off voltage
and the discharge cut-off voltage were set to 4.5 V and 2.5 V,
respectively.
Table 1 shows the results of performance evaluation of the lithium
secondary batteries of Example 1 and Comparative Example 1.
However, the results of evaluation of cycle life, charge-discharge
efficiency corresponding to the ratio of the amount of discharge
current to the amount of charge current, and energy density
(discharge capacity) per unit weight of the battery of Example 1
are standardized based on the values of 1.0 of Comparative Example
1.
TABLE 1 ______________________________________ Cycle life 1.3
Charge-discharge efficiency 1.1 Energy density 1.2
______________________________________
The results shown in Table 1 reveal that the use of the anode of
Example 1 form of the secondary battery increases the cycle life
and charge-discharge efficiency, and permits the formation of the
lithium secondary battery having high energy density.
EXAMPLE 2
In this example, a lithium secondary battery having the structure
shown in FIG. 7 was formed by the same method as in Example 1
except that an anode was formed by a different method,
(1) Procedure for Forming the Anode
After a nickel foil was washed with acetone, the surface of the
nickel foil was dipped in an ethanol solution of lecithin, dried
and then subjected to surface treatment. On the other hand,
tetrahydrofuran and a nematic liquid crystal,
p-n-phenyl-p'-cyanobiphenyl, were mixed with poly(p-phenylene) to
prepare paste. The thus-prepared paste was coated on the nickel
foil which was treated as described above and then dried to form
the nickel foil coated with a resin layer. The thus-obtained resin
layer-coated nickel foil was gradually heated to 800.degree. C. and
burned at this temperature in a stream of argon gas, to form the
anode.
The observation of the surface of the thus-formed anode under an
electron microscope showed that pores having a diameter of 3
microns or less are oriented substantially perpendicularly to the
nickel foil. The porosity calculated from an electron
microphotography was 60%.
The secondary battery was formed in the same manner as in Example 1
except that the anode formed in this example was used.
COMPARATIVE EXAMPLE 2
In this comparative example, a secondary battery was formed by the
same method as in Example 2 except that an anode was formed by a
different method.
(1) Procedure for Forming the Anode
Poly(p-phenylene) was gradually heated to 800.degree. C. and burned
at this temperature in a stream of argon gas, and then ground to
prepare a carbonaceous powder. The observation of the thus-obtained
carbonaceous powder under an electron microscope showed no oriented
pore.
After 5 wt % of polyvinylidene fluoride powder was mixed with the
thus-obtained carbonaceous powder, N-methyl pyrrolidone was added
to the mixture to prepare paste. The resultant paste was coated on
a copper foil, dried and then dried at 150.degree. C. under reduced
pressure to prepare the anode.
The secondary battery was formed in the same manner as in Example 2
except that the anode formed as described above was used.
X-ray diffraction of the carbonaceous powders used for the anodes
of Example 2 and Comparative Example 2 reveals that the ratio of
the half width (radian) of the (002) peak of Example 2 to the half
width of Comparative Example 2 is 0.66, and that the carbonaceous
powder of Example 2 is more graphitized than the carbonaceous
powder of Comparative Example 2.
Table 2 shows the results of performance evaluation of the lithium
secondary batteries formed in Example 1 and Comparative Example 2.
Performance evaluation was carried out in the same manner as in
Example 1, and the evaluation results of Example 2 are standardized
based on the values of 1.0 of Comparative Example 2.
TABLE 2 ______________________________________ Cycle life 1.1
Charge-discharge efficiency 1.2 Energy density 1.3
______________________________________
The results shown in Table 2 indicate that the use of the anode of
Example 2 for the secondary battery permits the formation of the
good lithium secondary battery, as in Example 1.
EXAMPLE 3
In this example, a lithium secondary battery having the sectional
structure shown in FIG. 7 was formed by the same method as in
Example 1 except that an anode was formed by a different
method.
(1) Procedure for Forming the Anode After tetrahydrofuran and a
ferroelectric liquid crystal
p-hexyloxybenzylidene-p'-amino-2-chloropropylcinnamate were mixed
with poly(2,6-naphthalene) to prepare paste, the thus-prepared
paste was coated on a rubbed copper foil, and then dried. The
thus-obtained resin-coated copper foil was heated to 140.degree. C.
in an atmosphere of nitrogen gas, and then gradually cooled to room
temperature through temperature ranges of smectic A phase and
smectic C phase of the ferroelectric liquid crystal with
application of a magnetic field of 1 terrace, to orientate the
ferroelectric liquid crystal. The copper foil was then washed with
ethanol and dried to prepare the copper foil coated with the resin
layer having oriented pores. The thus-obtained resin layer-coated
copper foil was gradually heated to 800.degree. C. and burned at
this temperature in a stream of argon gas, to form the anode.
The observation of the surface of the anode formed as described
above on an electron microscope showed pores which had a diameter
of 10 microns or less and which were perpendicularly oriented. The
porosity calculated from an electron microphotography was 40%.
The secondary battery was formed in the same manner as in Example 1
except that the anode formed by the above method was used.
COMPARATIVE EXAMPLE 3
In this comparative example, a secondary battery was formed by the
same method as in Example 1 except that an anode was formed by a
different method.
(1) Procedure for Forming the Anode
Poly(2,6-naphthalene) was gradually heated to 800.degree. C. and
burned at this temperature in a stream of argon gas, and then
ground to prepare a carbonaceous powder. The observation of the
thus-obtained carbonaceous powder under an electron microscope
showed no oriented pores.
After 5 wt % of polyvinylidene fluoride was mixed with the
carbonaceous powder, N-methyl pyrrolidone was added to the
resultant mixture to prepare paste. The thus-obtained paste was
coated on a copper foil, dried and then dried at 150.degree. C.
under reduced pressure to form an anode.
The secondary battery was formed in the same manner as in Example 3
except the anode formed by the above method was used.
X-ray diffraction of the carbonaceous powders used for the anodes
of Example 3 and Comparative Example 3 revealed that the ratio of
the half width (radian) of the (002) peak of Example 2 to the half
width of Comparative Example 3 is 0.84, and that the carbonaceous
powder of Example 3 is more graphitized than the carbonaceous
powder of Comparative Example 3.
Table 3 shows the results of performance evaluation of the lithium
secondary batteries formed in Examples 3 and Comparative Example 3.
The evaluation results of Example 3 are standardized based on the
values of 1.0 of Comparative Example 3.
TABLE 3 ______________________________________ Cycle life 1.1
Charge-discharge efficiency 1.2 Energy density 1.4
______________________________________
The results shown in Table 3 indicate that the use of the anode of
Example 3 for the secondary battery permits the formation of the
good lithium secondary battery, as in Example 1.
EXAMPLE 4
A lithium secondary battery having the sectional structure shown in
FIG. 7 was formed by the same method as in Example 1 except that an
anode was formed by a different method.
(1) Procedure for Forming the Anode
Water, 1,4-dioxane and a diacetylene derivative,
2,4-hexadyine-1,6-diol-bis-phenylurethane were mixed with polyvinyl
alcohol to prepare paste. The thus-prepared paste was irradiated
with ultraviolet rays by using a high-pressure mercury lamp for 3
hours to cause solid phase polymerization of the diacetylene
derivative and crosslinking of polyvinyl alcohol, followed by
drying under reduced pressure. The polydiacetylene-containing
polyvinyl alcohol was gradually heated to 800.degree. C. and burned
at this temperature in a stream of argon gas, and then ground to
prepare a carbonaceous powder. The observation of the resultant
carbonaceous powder on an electron microscope showed oriented pores
having a diameter of 15 microns or less. The porosity was 20%.
After 5 wt % of polyvinylidene fluoride was mixed with the
thus-obtained carbonaceous powder, N-methyl pyrrolidone was added
to the resultant mixture to prepare paste. After the thus-obtained
paste was coated on a copper foil, it was dried and then dried at
150.degree. C. under reduced pressure to form an anode.
The secondary battery was formed in the same manner as in Example 1
except that the anode formed as described above was used.
X-ray diffraction of the carbonaceous powder used for the anode of
Example 4 revealed that the ratio of the half width (radian) of the
(002) peak of the carbonaceous powder of Example 4 to the half
width of Comparative Example 1 is 0.37, and that the carbonaceous
powder of Example 4 is more graphitized than the carbonaceous
powder of Comparative Example 1.
Table 4 shows the results of performance evaluation of the lithium
secondary batteries formed in Examples 4 and Comparative Example 1.
The evaluation results of Example 4 are standardized based on the
values of 1.0 of Comparative Example 1.
TABLE 4 ______________________________________ Cycle life 1.4
Charge-discharge efficiency 1.2 Energy density 1.2
______________________________________
The results shown in Table 4 indicate that the use of the anode of
Example 4 for the secondary battery permits the formation of the
good lithium secondary battery, as in Example 1.
EXAMPLE 5
In this example, a lithium secondary battery having the structure
shown in FIG. 7 was formed. A carbonaceous material having oriented
pores and containing a cathode active material dispersed therein
was used for a cathode. The procedure for forming each of the
components of the battery and the assembly of the battery are
described below.
(1) Procedure for Forming the Cathode
After electrolytic manganese dioxide and lithium carbonate were
mixed at a ratio of 1:0.4, the resultant mixture was heated at
800.degree. C. and then ground to prepare a lithium-manganese oxide
powder. After water and the thus-prepared lithium-manganese oxide
powder were added to polyvinyl alcohol and kneaded therewith, a
methanol solution of a nematic liquid crystal,
p-methoxybenzylidene-p'-n-butylaniline, was mixed with the
resultant mixture, and the solvent was evaporated by drying at
45.degree. C. under reduced pressure. After the liquid crystal was
removed by washing with methanol at 30.degree. C., the residue was
dried and sintered at 800.degree. C. in an atmosphere of nitrogen
gas to prepare the carbonaceous material containing the
lithium-manganese oxide dispersed therein. The observation of the
thus-formed carbonaceous material containing lithium-manganese
oxide dispersed therein under an electron microscope showed
oriented pores. The porosity was 30%.
After the thus-obtained carbonaceous material containing
lithium-manganese oxide dispersed therein was ground, 5 wt % of
polyvinylidene fluoride powder was mixed with the resultant powder,
and N-methyl pyrrolidone was added thereto to prepare paste. After
the thus-obtained paste was coated on an aluminum foil and dried,
and then dried at 150.degree. C. under reduced pressure to form the
cathode.
(2) Procedure for Forming the Anode
After 5 wt % of polyvinylidene fluoride powder was mixed with
natural graphite fine powder, N-methyl pyrrolidone was added to the
resultant mixture to prepare paste. The thus-obtained paste was
coated on a copper foil and dried, and then dried at 150.degree. C.
under reduced pressure to form the anode.
(3) Procedure for Forming an Electrolyte
A solvent was prepared by mixing equivalent ethylene carbonate (EC)
and dimethyl carbonate (DMC), from which moisture was sufficiently
removed. 1M (mol/l) of lithium tetrafluoroborate was dissolved in
the thus-obtained solvent to form the electrolyte.
(4) Separator
A microporous film of polypropylene was used as the separator.
(5) Assembly of the Battery
The separator holding the electrolyte was held between the anode
and the cathode, and inserted into a cathode can made of titanium
clad stainless steel. An insulating packing made of polypropylene
and an anode cap made of titanium clad stainless steel were placed
in turn on the cathode can, and then caulked to form the lithium
secondary battery.
COMPARATIVE EXAMPLE 4
In this comparative example, a secondary battery was formed in the
same manner as in Example 5 except that the cathode was prepared by
the same method as in Example 1.
Table 5 showed the results of performance evaluation of the lithium
secondary batteries formed in Example 5 and Comparative Example 4.
The performance evaluation was performed by the same method as that
employed in Example 1. The evaluation results of Example 5 shown in
Table 5 are standardized based on the values of 1.0 of Comparative
Example 4.
TABLE 5 ______________________________________ Cycle life 1.2
Charge-discharge efficiency 1.1 Energy density 1.1
______________________________________
The results shown in Table 5 indicate that the use of the cathode
of Example 5 having oriented pores for the secondary battery
permits the formation of the good lithium secondary battery, as in
Example 1.
EXAMPLE 6
In this example, a lithium secondary battery having the structure
shown in FIG. 7 was formed by the same method as that employed in
Example 5 except that a cathode was formed by a different
method.
(1) Procedure for Forming the Cathode
After electrolytic manganese dioxide and lithium carbonate were
mixed at a ratio of 1:0.4, the resultant mixture was heated at
800.degree. C. and then ground to prepare a lithium-manganese oxide
powder. A nonionic surface active agent (polyoxyethylene sorbitan
triolate) and the lithium-manganese oxide powder prepared as
described above were added to a 1,2-dichloroethane solution of
polyacenaphthylene, followed by agitation. After a 5% m-cresol
solution of racemized L- and D-type poly(.gamma.-benzyl-glutamate)
was mixed with the resultant mixture, the solvent was gradually
evaporated to manifest a liquid crystal phase. The liquid crystal
phase was then sintered at 800.degree. C. in a stream of nitrogen
gas to prepare a carbonaceous material containing lithium-manganese
oxide dispersed therein. The observation of the thus-formed
carbonaceous material containing the lithium-manganese oxide
dispersed therein showed oriented pores. The porosity was 30%.
After the thus-obtained carbonaceous material containing
lithium-manganese oxide dispersed therein was ground, and 5 wt % of
polyvinylidene fluoride powder were mixed with the resultant
powder, and N-methyl pyrrolidone was added thereto to prepare
paste. The resultant paste was coated on an aluminum foil and
dried, and then dried at 150.degree. C. under reduced pressure to
form a cathode. The secondary battery was formed in the same manner
as in Example 5 except that the cathode formed in this example was
used.
Table 6 showed the results of performance evaluation of the lithium
secondary batteries formed in Example 6 and Comparative Example 4.
The evaluation results of Example 6 shown in Table 6 are
standardized based on the values of 1.0 of Comparative Example
4.
TABLE 6 ______________________________________ Cycle life 1.2
Charge-discharge efficiency 1.1 Energy density 1.1
______________________________________
The results shown in Table 6 indicate that the use of the cathode
of Example 6 for the secondary battery permits the formation of the
good lithium secondary battery, as in Example 1.
EXAMPLE 7
In this example, a lithium secondary battery having the structure
shown in FIG. 7 was formed by the same method as that employed in
Example 5 except that a cathode was formed by a different method
from Example 5.
(1) Procedure for Forming the Cathode
A 2M (mol/l) aqueous solution of nickel acetate and 1 m (mol/l)
aqueous solution of lithium citrate were mixed at a ratio of 1:1,
and the resultant mixture was then dried by a spray dryer, heated
at 800.degree. C. in air and ground to prepare a lithium-nickel
oxide powder. A nickel foil was washed with acetone, and then
subjected to surface treatment by dipping the nickel foil in an
ethanol solution of lecitin and then drying.
Tetrahydrofuran, a nonionic surfactant (polyoxyethylene sorbitan
triolate), the lithium-nickel oxide powder obtained as described
above, and a discotic liquid crystal
2,3,6,7,10,11-hexamethoxytriphenylene were mixed with poly(furfuryl
alcohol) to prepare paste.
The thus-prepared paste was coated on the treated nickel foil and
dried to form the nickel foil coated with a resin layer.
Thus-obtained resin layer-coated nickel foil was gradually heated
to 800.degree. C. and burned at this temperature in a stream of
argon gas to form the cathode. The observation of the surface of
the cathode formed as described above under an electron microscope
showed pores which had a diameter of 3 microns or less and which
were oriented perpendicularly to the surface of a collector. The
porosity calculated from an electron microphotography was 30%.
The secondary battery was formed in the same manner as in Example 5
except that the cathode formed in this example was used.
COMPARATIVE EXAMPLE 5
In this comparative example, a cathode was formed by using a
cathode active material which was prepared by a different method
from Example 7, and the same anode as Example 4 was used.
(1) Procedure for Forming the Cathode
Nickel carbonate and lithium nitrate were mixed at a molar ratio of
1:1, and the resultant mixture was heated at 800.degree. C. to
prepare lithium-nickel oxide. 3 wt % of carbonaceous powder of
acetylene black and 5 wt % of polyvinylidene fluoride powder were
mixed with the thus-prepared lithium-nickel oxide, and N-methyl
pyrrolidone was added to the resultant mixture to obtain paste.
After the thus-obtained paste was coated on an aluminum foil and
dried, and then dried at 150.degree. C. under reduced pressure to
form a cathode. The observation of the surface of the cathode on a
scanning electron microscope shows no oriented pore.
A secondary battery was formed in the same manner as in Comparative
Example 4 except that the cathode formed as described above was
used.
Table 7 showed the results of performance evaluation of the lithium
secondary batteries formed in Example 7 and Comparative Example 5.
The evaluation results of Example 7 shown in Table 7 are
standardized based on the values of 1.0 of Comparative Example
5.
TABLE 7 ______________________________________ Cycle life 1.2
Charge-discharge efficiency 1.1 Energy density 1.2
______________________________________
The results shown in Table 7 indicate that the use of the cathode
of Example 7 for the secondary battery permits the formation of the
good lithium secondary battery, as in Example 1.
EXAMPLE 8
A secondary battery was formed in the same method as in Example 1
except that the same anode as that formed in Example 1 and the same
cathode as that formed in Example 5 were used. Table 8 shows the
results of performance evaluation of the secondary batteries formed
in Example 8 and Comparative Example 1. The values shown in Table 8
are values of Example 8 which are standardized based on 1.0 of
Comparative Example 1.
TABLE 8 ______________________________________ Cycle life 1.4
Charge-discharge efficiency 1.2 Energy density 1.3
______________________________________
Although, in Examples 1 to 8, lithium-manganese oxide or
lithium-nickel oxide was used as the cathode active material, the
present invention is not limited to these materials, and various
materials such as lithium-cobalt oxide, lithium-vanadium oxide and
the like can also be used as the cathode active material. Although,
in Examples 1 to 8, the same electrolyte was used, the present
invention is not limited to this.
The present invention is not limited to the above examples
including the constructions and the structures of secondary
batteries of the examples. Various modifications and combinations
can, of course, appropriately be made within the scope of the gist
of the present invention.
As described above, since the present invention is capable of
forming a cathode or anode having an increased pore volume for a
lithium secondary battery which employs intercalation and
deintercalation reaction of lithium ions, it is possible to
smoothly effect electrochemical reaction with substantially low
current density accompanied with charge and discharge, and permit a
flow of large current. In addition, if the present invention is
applied to a cathode, the area of contact between a cathode active
material and a carbonaceous material used as a conduction auxiliary
can be increased, thereby improving the current collecting ability
of the cathode.
Further, the present invention is capable of forming a lithium
secondary battery having a long cycle life, a high charge-discharge
efficiency and a high energy density.
The formation method of the present invention is capable of easily
forming a anode and a cathode each of which comprises a
carbonaceous material having oriented pores in a simple step.
* * * * *